We are studying a new class of matrix-derived glycoproteins which regulate embryogenesis and wound repair. In vitro, these glycoproteins control the assembly of the extracellular matrix and influence cell behavior by modulating cell adhesion, growth, migration, matrix production and differentiation. These proteins bind the cells to the matrix and specific attachment proteins exist for each cell type and matrix. It is also possible to control or suppress the growth and differention of certain cells by adding attachment glycoprotein not normally present in the tissue. For example, the addition of basement membrane-derived attachment glycoprotein inhibits the growth of fibroblasts and connective tissue cells and induces the outgrowth and differentiation of neurites from explants of human sensory spinal ganglia. Through these biological activities, these attachment glycoproteins can control which cells will populate a matrix during development and can effect repair reactions necessary to replace damaged tissue.